Suzaku Observation of the Eastern X-ray Lobe of SS 433
Hideki Uchiyama,1 Yuta Kanbe2
1

Faculty of Education, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka, 422-8529, Japan
Faculty of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka, 422-8529, Japan
E-mail(HU): uchiyama.hideki@shizuoka.ac.jp

2Abstract
We observed the eastern X-ray robe of SS 433 with Suzaku. The non-thermal component of the Xray spectrum cannot be described by a simple power-law model, but requires a cutoff around 8 keV. We
also found that the cutoff energy decreases as the distance from SS 433 increases. It is probably due tosynchrotron cooling of electrons accelerated near SS 433. Based on this, the magnetic field around thelobe B is limited to be weaker than ∼ 75 µG. The high-energy electrons traveled a distance of ∼9.6 pc
among 650 yr if B =10 µG. The bulk velocity of the jet, which is 0.26 c near the compact object, keeps∼ 0.05c after the jet traveled a distance of ∼ 35 pc.
Key words: ISM: jets and outflows — X-rays: individuals:(SS433) — X-rays: individuals:(W50)(./)%0,1!

5.0+,-$%&'()))*!

1. Introduction
SS 433 is an X-ray binary and its compact object is oneof the most famous blackhole candidates. Jets with avelocity of 0.26 c exist near the compact object (Margon 1984). A radio-shell supernova remnant (W50) is
associated with SS433. The shell is extended toward theeast and west. It is thought that the interaction with thejets caused the extended structure. Diffuse X-ray emission is also associated with the extended radio shell. Onthe east side, there is a bright structure like a knot (e.g.
Yamauchi et al. 1994).
To reveal the detail structure of the X-ray emission, weobserved the eastern X-ray lobe for 107 ks with Suzaku
XIS whose features are large effective area and a low
stable non-X-ray background. The observed position isabout 35 arcmin away from SS 433. The X-ray image isshown in figure 1.

D!

C!

4.9

r =33’.5

r =27’.5(~44 pc)!

4.8

r =39’.5!

2. Spectrum from the Entire Field of View
We made a spectrum from the entire field of view ofXIS. It is shown in figure 2. Models of the Galaxy
background (Uchiyama et al. 2013) and the cosmic Xray background (CXB, Kushino et al. 2002) were addedfor fitting. As reported by Brinkmann et al. (2007), thespectrum of the X-ray lobe consists of a optically-thinthermal plasma component (APEC, Smith et al. 2001)
and a non-thermal component with interstellar absorption.
If we used a simple power law as the non-thermal
component, large residual appeared above 3 keV. Whenthe non-thermal component is a cutoff power law withA!

B!

r =45’.5 (~73 pc)!
288.7

288.6

Distance fromSS433!
288.5

288.4

"#$%&'()))*!

Fig. 1. X-ray Image of the observed region with Suzaku XIS. The
regions from which spatially divided spectra are extracted are also
shown (see section 3.).

!./08A6A:B6+4C:B$

9.0:834-5&'$*.57.0408$;*/8.<67.=4-6'&=>$!"#234-5&'6*.57.0408$!"!#%&'&()$#&*+,-./01$!"#$;D&8&:E.14'>FG--.-$$?@57'467.=4-6'&=$

"%!"
!$$

HIF1J.JKJLIBMFBMILBJNB$!

"#!/8.<67.=4-6'&=$%!
!%

HIF1J.JKJLBNOFBMBLBJBB$!$#%&'()*+,-./)01

Fig. 2. Spectrum from the entire field of view. The residuals of thefitting with simple or cutoff power-law models for the non-thermalcomponents are also shown.

hνcutof f ∼ 8 keV, the residual disappeared and reduced
χ2 also became much smaller (figure 2). We, for the firsttime, found that the non-thermal component requires acutoff.
3. Spatial Profile of the Cutoff Energy
We made spectra from the regions of A, B, C and D
shown in figure 1 to study the spatial profile of the cutoff energy hνcutof f . The regions of A, C and D are annuluses centered at SS 433. The region B corresponds
to the bright knot-like structure but its spectrum is notmuch different from those of the other region. We fitted
4 spectra simultaneously. The temperature of the thermal component, the photon index of the non-thermalcomponent and interstellar absorption were linked for all
the regions. The normalizations of the components andhνcutof f of determined independently for each region.
The obtained spatial profile of hνcutof f is figure 3. Thehνcutof f decreases as the distance from SS 433 increases.
The spatial dependence of photon index was reported byprevious studies (Yamauchi et al. 1994, Brinkmann etal. 2007) but we found that it can be explained by thechange of hνcutof f .
4. Discussion
The probable origin of the non-thermal component issynchrotron radiation of high-energy electrons. The cutoff is probably due to the synchrotron cooling of the elec-Fig. 3. Spatial profile of hνcutof f obtained by simultaneous fittingof spectra from region A–D.

trons. The higher the electron energy, the shorter thecooling time. The spatial change of the cutoff hνcutof fshows that the electrons accelerated near SS 433 moveoutward while cooling. Our result suggests that theacceleration occurs outside of the field of view of thisSuzaku observation.
Figure 3 indicates that the electrons traveled the distance between A and C, 9.6 pc (the distance between theSun and SS 433 is 5.5 kpc; Blundell & Bowler 2004), inthe cooling time of electron which radiate photons withthe energy of hνcutof f ∼ 5.5 keV typically. The upper
limit of the magnetic field B near the eastern X-ray lobe
is obtained from the constraint that the speed of electrons is slower than the light velocity. Therefore, B is
weaker than 74µ G. A similar calculation between C andD gave a limit of B < 79µ G.
Hayashi et al. (2009) reported that the lower limit of
the interstellar magnetic field in the western X-ray lobe
is 6.8 µG from the TeV γ-ray observation. Considering
this and the upper limit obtained above, we assumed that
B=10 G. If there is no reacceleration, the electrons arethought to be traveled 9.6 pc during ∼ 600 yr (A–C) or∼ 700 yr (C–D). This result shows that the bulk velocityof the jet keeps ∼ 0.05 c after the jet traveled a distanceof ∼ 35 pc. This is close to a expected velocity after
standing shock of the velocity of 0.26 c, 0.26/4 = 0.063 c.
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